Well, also it is about gay culture and how it is represented in anime. Compared to live action versions of gay culture, anime is pretty chaste (the non-hentai part). The other problem is that yaoi gets very few anime made as a genre. I mean the average anime is pretty bad, so the average yaoi anime is going to likely be bad also. That said, it does seem that yaoi focus more on the shallow physical aspects than most romance anime, in general. Even Given which was one of the more high quality yaoi, they moved pretty fast to the physical stuff.
Yuri anime are bad in a different way in that they tend to be dominated by kawaii, lolis, and moe characters (not that I complain... I love that sh!t).